Manufacturing techniques that are common to the microprocessor, computer and electronics industries have found a variety of new outlets. For example, in the marriage of semiconductor fabrication techniques with biological research, a variety of chip based analytical systems have been developed, i.e., oligonucleotide arrays (See U.S. Pat. No. 5,143,854 to Pirrung et al.) High Throughput screening devices employing microfluidic technology (See U.S. Pat. No. 5,942,443), and lower throughput separations based microfluidic analysis devices (See U.S. Pat. No. 5,976,336).
A number of different fabrication methods have been described for producing microfluidic devices, including photolithography followed by wet chemical etching, injection molding or embossing of plastics, laser ablation, micromachining, and the like. Different fabrication techniques can have different advantages, depending upon the nature of the use that the finished device is to be put. However, for a large number of different applications, silica-based substrates are preferred, e.g., for their chemical inertness, optical properties, and the like. As such, a large proportion of microfluidic devices are fabricated using lithographic/wet chemical etching processes to produce the various features of the devices.
In a first aspect, the present invention provides a method of fabricating microstructures on a substrate. The method comprises providing a substrate layer having a first surface with a resist layer. First selected regions of the resist layer are exposed to an environment that renders the resist layer more or less soluble in a developer solution. The resist layer is then developed in the developer solution to expose selected regions of the substrate surface. Second selected regions of the resist layer are then exposed to an environment that renders the resist layer more or less soluble in the developer solution by aligning exposure of the second selected regions to the first selected regions. The first selected regions of the substrate surface are etched. Second selected regions of the resist layer are then developed to expose the second selected regions of the substrate surface. The first and second selected regions of the surface of the substrate are then etched.
Another aspect of the present invention is a substrate layer comprising microstructures on a first surface. The substrate layer is produced by a process comprised of providing the substrate layer with a first surface and a first resist layer. The first selected regions of the resist layer are exposed to an environment that renders the resist layer more or less soluble in a developer solution. The first resist layer is developed in the developer solution to expose first selected regions of the substrate surface. Second selected regions of the resist layer are exposed to an environment that renders the resist layer more soluble in the developer solution by aligning exposure of the second selected regions to the first selected regions. The first selected regions of the substrate surface are etched. The second selected regions of the resist are developed to expose second selected regions of the substrate surface. The first and second selected regions of the surface of the substrate are then etched to produce microstructures on the first surface of the first substrate layer.
A further aspect of the present invention is a substrate comprising a first surface, a first resist layer disposed on the first surface, first selected regions of the substrate surface having no resist layer disposed thereon, and second selected regions of the substrate surface. The second selected regions of the substrate surface are aligned with the first selected regions. The second selected regions comprise a developable resist layer.